The transfer of DNA between bacterial species is assumed to play an important role in the dissemination of antibiotic resistance. Unfortunately, little information is available on the extent of genetic transfer occurring in natural bacterial populations. Plaque biofilms offer an excellent opportunity to study genetic transfer mechanisms in an easily accessed multi-species population. Interspecies genetic exchange can involve the conjugal horizontal transfer of antibiotic resistance genes and other virulence factors, which may contribute to the development of periodontal infections resistant to therapy. Additionally, members of the oral flora have the potential to transfer antibiotic resistance to other pathogens that are transient colonizers of the mouth. There is a significant need for basic molecular studies into horizontal gene transfer in oral bacteria. This proposal will outline experiments to initiate molecular studies of the tetQ-encoding conjugal transposons present in members of the oral anaerobes Porphyromonas and Prevotella. The Specific Aims of this proposal are 1) to "capture" conjugative elements from clinical isolates and compare their structure and behavior through RFLP analysis and conjugation assays, and 2) to submit a representative element for DNA sequencing, and use the resulting information to develop a classification system for these elements, based on gene content and functional behavior. These studies will provide important insights into the distribution and functionality of horizontally transferred elements in the human oral flora. [unreadable] [unreadable]